Implements blueprint keystone-domain-configuration
Adds a provider able to configure multiple domains and two parameters in
keystone class to setup a working multi-domains configuration.
The keystone_config type has been refactored into a mixin to be shared
by keystone_config and keystone_domain_config.
The provider, even though it is inheriting from openstack_config (and
not keystone_config because it hard code the path), has required more
new code. The problem is that we have several configuration files to
work with (one per domain) which is unusual.
The self.prefetch method is required to check the current catalog. If
it's changing the Keystone_config[identity/domain_config_dir] we take it
directly into account without the need for another run.
Keystone_config[identity/domain_config_dir] configuration and the
associated directory are autorequired.
Change-Id: I5e4b298460ee592640af59ac9dcbefa3daf98098
07f19bd38a